The present invention relates to an airbag for use as a vehicle safety restraint and particularly to an airbag for use on the driver's side of a vehicle.
Driver's side airbags are traditionally mounted in the hub of a steering wheel. They are generally disc-shaped and formed of two pieces of fabric joined around their circumference. A hole is formed in the centre of one of the circular pieces to allow gas to pass into the airbag to inflate it in the event of a crash.
It is desirable in such airbags to control the inflation characteristics so as to limit the maximum extension of the airbag in the direction toward the vehicle driver, and to reduce the velocity of deployment of the airbag in the driver's direction to reduce the potential for injury to the driver from the airbag itself. For occupants sitting close to the airbag module the hazard of injuries are minimised by providing improved deployment kinematics.
Airbag inflation characteristics, including direction and velocity of deployment, are known to be influenced by the way that the airbag is folded into the airbag housing. It is also known that control can be influenced by providing tear lines by stitching through the two pieces of airbag fabric to join the front and back pieces of the airbag together.
U.S. Pat. No. 5,280,154 describes an example of tear line stitch patterns. Various embodiments are shown but in general the tear lines are arranged in concentric coaxial circles about the gas inlet hole. Some additional radial tear lines are also suggested.
However this arrangement does not produce optimum results in terms of smoothness of deployment, low axial deployment (towards the driver) speed, and cushion kinematics. In addition it results in high peak loads on localised areas of the cushion fabric resulting in localised fabric rupture.
It is an object of the present invention to produce an improved airbag particularly for a driver's side.
For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made to the accompanying drawings, in which: